Effects of Azosprillum bacteria and crop residue application on macronutrient uptake of barley under water stress conditions

The amount of macronutrients content is affected by various environmental factors such as severe water stress occurs after anthesis. Using of Azospirillum brasilense as a biofertilizer and crop residues for increasing soil organic matter are the two methods for reducing water stress in the farms. However, despite the favorite effects of Azospirillum brasilense and crop residues application for reducing negative effects of water stress, a few studies have been performed on regarding the effects of these factors on macronutrients uptake of barley in the warm and arid regions of Southern Iran. Therefore, the aim of this study was to investigate the effects of Azospirillum brasilense and wheat residues applications on macronutrients uptake of barley.

This research was conducted at the experimental farm of the Darab Agricultural College of Shiraz University. A split factorial experiment in a randomized complete block design with three replicates were carried out in 2017 - 2018 growing season. Treatments included: two levels of irrigation as the main plots [normal irrigation (IRN): irrigation based on the plant's water requirement up to the physiological maturity and the other factor was deficit irrigation (IRDI): irrigation based on the plant's water requirement up to the anthesis stage (cutting of irrigation after anthesis)]. Also, sub plots were two levels of crop residues [1. without residue, 2. returning 30% of wheat residues to soil] and four fertilizer sources [N0, no nitrogen fertilizer (control); N100, 100 kg N ha-1 (as urea); Bio + N50, Biofertilizer (Azospirillum brasilense) + 50 kg N ha-1 (as urea) and Bio, Biofertilizer (Azospirillum brasilense)].

Interaction of residue × nitrogen (N) source on barley grain N content showed that the highest and the lowest grain N content (161.7 and 43 kg ha-1, respectively) were achieved in without residue and the Bio + N50 and in with residue and Bio treatments, respectively. Also, the straw N content was affected by the interaction of irrigation regime × residue × N source. The highest N content of straw was obtained in IRDI, with residue and N100 treatments (62.9 kg ha-1) and the lowest was achieved in IRDI, with residue and N0 treatments (5.7 kg ha-1). The highest grain and straw phosphorus (P) content (1.35 and 1.12 kg ha-1, respectively) was obtained by the Bio + N50 and N100 treatments, respectively. The irrigation regime × residue × N source interaction showed that the highest and the lowest grain potassium (K) content (12.6 and 4.0 kg ha-1, respectively) was belonged to IRDI, without residue and N100 treatments and IRDI, with residue and N0 treatments, respectively. Also, irrigation × N source interaction showed that the highest K content of straw (114.4 kg ha-1) was achieved in IRN and Bio + N50 treatments and the lowest K content of straw (33.3 kg ha-1) was observed in IRDI and Bio treatments.

Based on the findings of this experiment, the Bio + N50 treatment is appropriate for achieving the maximum macronutrients content of barley in IRN conditions. Therefore, with respect to environmental and economic considerations and achieving high levels of barley macronutrients content, this fertilizer regime is recommended.